Higher frequency applications operate in the millimeter-wave frequency range of 30 GHz to 300 GHz, and may provide wireless communications at unidirectional data rates exceeding 2.0 Gigabytes per link. Examples of these applications include Wireless Display (WiDi), wireless docking, wireless probes for post-silicon validation, and wireless chip-to-chip communications within and between platforms.
For these applications, several antenna structures small enough to fit within a package substrate of a wireless die have been proposed. In order to achieve a desired bandwidth, many of these antenna structures require several package build-up layers formed using expensive fabrication technology, such as low temperature co-fired ceramic (LTCC), or must be placed inside an air cavity within the package, leading to fabrication and reliability problems. Standard packages require thin build-up layers to enable thin vias (via aspect ratio should be close to one) and dense interconnects. However, this requirement conflicts with a requirement for thick, almost evenly spaced layers needed to obtain wide-band, high-efficiency, multi-layer antenna designs, such as stacked patch antennas. One solution to overcome these conflicting requirements is to implement several thin layers to enable small vias and at the same time obtain an overall thickness large enough for wide-band antenna designs. This solution, however, leads to an increase in package cost and reduction in yield. Also, the resulting ultra-thick packages conflict with a goal for achieving ultra-thin portable devices, such as tablets, smartphones and wearable computing devices.